Shaft-hub joint for transmission of torque between two equiaxial machine parts

ABSTRACT

The invention concerns a shaft-hub joint between two equiaxial machine parts for transmission of high torques in a power train--a first machine part on the power input end and a second machine part of the power output end. The machine parts are joined to each other in a fashion movable relative to each other but rotationally fixed, and a positive-locking overload relief mechanism is provided between the machine parts, the individual locking elements of which are prestressed in the sense of locking. The overload relief mechanism locks the two machine parts against axial thrust up to a specific adjustable limit value whereby the positive locking will be eliminated when the limit value is exceeded. The interlocking elements comprise bolts with a head surface beveled in wedge fashion.

BACKGROUND OF THE INVENTION

The invention concerns a shaft-hub joint for transmission of torquesbetween two equiaxial machine parts.

It is known that in power trains, for example such for use in rollingmills where the torque generated by the motor is transmitted via shafttrains--in a rolling mill, e.g., the working roll is powered through ajointed shaft--disturbances on the machine end being driven due to whicha transmission of torque from the power input to the power output may beinterrupted at continued operation of the power source cause adeformation in the power train, due to torsion, and eventual torsionalfracture. The torsional fracture shows in the extreme case a fracturepattern of 45° to the axis of torsion, due to the tensile stressesoccurring in twisting. In the case of the rolling mill, for example,torque transmission between the power source and working roll isinterrupted in the case of working roll jamming. Subsequent to thefracture, i.e., in the example after separation of the working roll fromthe power source and with simultaneous continued operation of the powersource, the fracture face on the side of the drive train that is stilljoined to the power source is twisted relative to the now stationaryfracture face located on the side of the working roll. Due to thesuperimposition of the fracture faces and due to the differences ininertia and speed of rotation between the parts of the power train thathave been created by the fracture--the one connected to the power sourceand that joined to the working roll--the part joined to the power sourceundergoes an axial shift in its own direction. The continued drivemotion imparted by the motor and the obliquely fashioned fracture leadgenerally to the occurrence of high axial forces which bring about apositional shift of individual elements of the power train, in theextreme case a heaving of the components out of their anchoring.

A known solution for avoidance of such incidents consists in fashioningthe joint between power source and element being driven, not integrallyin the form of a shaft train, but in at least in two parts, and to jointhese two parts in such a way that the torque transmission will berealized while also appropriate overload relief mechanisms are allowedto become effective which at high axial forces interrupt thetransmission of torque. In the prior solutions, an element is used as asafety clutch which also functions as the rotationally fixed jointbetween the two parts, for example the two parts of the shaft train. Thesafety clutch serves the transmission of high torques and is providedwith a system for torque limitation, such as is known for instance fromDE 29 23 902.

This clutch comprises at least one thin-walled sleeve forming an axiallyextending wall of an essentially annular chamber which can be acted uponby a pressure medium so as to deform the sleeve essentially elasticallyin the radial direction and cause it to bind with a surface of anelement on which the clutch is mounted. There are two options availablefor that purpose. In one option, the clutch becomes effective betweenthe two machine parts to be joined, in that the clutch is designed as abushing that consists of two sleeves welded to each other and whosecavity can be acted upon by a pressure medium, deforming the sleevesradially and locking the two machine parts onto each other. In thesecond option, the clutch embraces both machine parts and causesfrictional engagement between both by deformation of only one sleeve.Bordering on the annular chamber is a duct arrangement with which asafety or clutch relief mechanism is coordinated. The relative motionbetween the surfaces of the two machine parts which are to be joined byfrictional engagement or a specific torsional deformation of same can becaused to enter a state in which the pressure medium contained in theannular chamber can escape from it through the duct arrangement, therebyrelieving the annular chamber. Hence, the clutch is adjusted to thedesired torque of release. If this torque is exceeded due to anoverload, slippage of the clutch occurs. The transmitted torquediminishes, since the effective coefficient of adhesive frictiontransforms to a coefficient of sliding friction. A relative motionbetween the shaft and hub takes place in the peripheral direction.Mounted for instance on the shaft, a shear ring shears off a shear valvewhich communicates with the duct arrangement or the annular chamber ofthe clutch.

With the shear valve(s) sheared off, the highly pressurized oil canexpand freely, and the transmittable torque drops within a fewmilliseconds to zero.

To safeguard against axial force overloads, the clutch is adjusted to anappropriate admissible axial force to be transmitted, i.e., the internalpressure of the annular chamber is so set that with it the frictionalengagement can be maintained only up to the level of the critical axialforce. As the admissible axial force is exceeded, for example due to afracture, the frictional engagement is eliminated and supplanted by arelative motion in the axial direction between the clutch and theelements joined to it. The disadvantage of this embodiment is that theclutch must be set to an appropriate axial force and designedaccordingly. A simultaneous transmission of high torques with the sameclutch can be realized only in rarest cases, since the surface pressuresbetween clutch, shaft and hub that are required from transmission of thedesired torque and the still admissible axial force may vary from oneanother depending on conditions of application. Owing to the equality ofthe forces that are required for elimination of the frictionalengagement in the peripheral direction and in the axial direction, andowing to the desire to actuate the clutch relief mechanism at axialforces that are already relatively low as compared to the peripheralforce, only low torques can be transmitted with clutches of such design.

Another option is relieving in the case of such a clutch the system fortorque limitation, i.e., for release of the frictional engagement, at aselected axial force, by measuring the magnitude of the axial forces andtransforming the measured value to a signal for release of the safetymechanism for torque limitation. But this option is characterized by avery high metrological and control expense, since the response timesmust be very short.

Therefore, the problem underlying the invention is to so advance ashaft-hub joint of the general type just described such that theaforementioned disadvantages will be eliminated. The shaft-hub jointshould be suited for transmission of high torques, for instance for usewith jointed shafts or universal shafts, and the overload reliefmechanism is to be able to react to already low axial forces.

The structural conversion should be such that the overload reliefmechanism will respond at a specific magnitude of the effective axialforce. In doing so, the emphasis is on a low-cost realization ofstructure and function, with a small number of components of simpledesign. The entire arrangement is meant to excel by having a lowmanufacturing and assembly expense as well as simple and quick resettingafter a response event.

SUMMARY OF THE INVENTION

This problem is solved by providing a positive-locking overload reliefmechanism comprising at least one interlocking element provided betweenthe machine parts locking the machine parts against axial thrust up to agiven adjustable limit in value, wherein positive locking is eliminatedwhen the limit value is exceeded. The interlocking element comprises ahead having surfaces beveled in wedge fashion viewed in cross section,the interlocking element being supported by the first machine part andpressed by a prestress force into a receiving recess in a surface of thesecond machine part.

The previously known two-part design of a joint between power source andelement to be driven, in the form of a rotationally fixed joint betweenthe two parts, is replaced by a rotationally fixed joint with axiallength equalization. The additional employment of an overload reliefmechanism which responds only upon exceeding an adjustable limit valueof a specific axial force magnitude makes it possible to avoid in thecase of a fracture or very high axial forces a high stress upon theindividual elements of the power train. The axial force is compensatedfor by the shift of the two machine parts relative to each other bymeans of the axial length equalization, which is triggered by the actionof the overload relief mechanism. Bolts or pins with a head surfacebeveled in wedge fashion are used as interlocking elements. For example,the entire head may be conic or the head surface may be wedge-shapedonly in cross-sectional view. The bolts themselves may be fashioneddifferently; for example, they may have a circular or square crosssection in the end view.

The interlocking elements are supported by one of the two machineparts--for instance by the first machine part--and forced into matingreceiving recesses in the other part, presently in the second machinepart. The geometry of the interlocking elements enables transmission ofhigh axial forces, which in comparison to conventional interlockingelements expresses itself in size reductions. The complementarywedge-shaped recesses impose on the manufacturing and assembly accuracylower requirements than in the case of other positive-locking joints,since these joints are capable of equalizing variations up to themillimeter range.

Furthermore, a more exact adaptation is possible to specific axialforces that must not be exceeded. The use of bevel bolts, therefore, ischaracterized by reduced wear and greater availability of the entireoverload relief mechanism.

The number of interlocking elements and/or the change ingeometry--specifically of the bevel angle--and/or the magnitude of theprestress force for the interlocking elements allow adjusting the limitvalue of the axial force; exceeding said limit value causes a responseof the overload relief mechanism, that is, the shift of the two machineparts relative to each other.

The split design of the second machine part chosen in a preferredembodiment--i.e., subdividing the second machine part in two sectionswhere the first section is joined to the first machine part directly byrotationally fixed joint, but with the option of axial lengthequalization, and where the second section (signified only as a hollowbody in the example) is joined directly only to the interlockingelements of the overload relief mechanism, and indirectly to the firstsection--enables the provision of a curtailed axial shiftability betweenthe two sections. Damping elements, specifically spring elements, arepreferably provided between the two sections.

The split design with the option of a reduced axial backlash between thetwo sections and the arrangement of spring elements, preferably disksprings, between these two sections offer several advantages:

1) The overload relief mechanism, specifically the interlockingelements, are extensively kept free of dynamic stresses.

2) Axial shifts due to axial forces of a magnitude smaller than theadjusted limit value of the axial force are compensated for, or damped.

3) The interlocking elements have in idling no centering effect on bothmachine parts.

The spring elements between the two sections of the second machine partare arranged in a sealed space featuring at least two lubricantchannels--a lubricant feed channel and a lubricant removal channel.During operation, the space is filled with a lubricant, preferablygrease. At an axial shift caused by a high axial force and leading to aresponse of the overload relief mechanism, the lubricant proceeds viathe removal channel to the interior of the second section and fromthere, due to centrifugal force effect, to channels which communicatedirectly with the receiving recesses in order to lubricate theappropriate receiving recess surfaces at the moment of theirdisengagement.

Usable as interlocking elements include in this case also cylinderrollers, balls or bolts (pins) with an oblique bevel surface (bevelbolts), with the latter enjoying preference because the axial forces aretransmitted here to the bevel bolt via large surfaces, whereas highHertz stresses occur when using cylinder rollers and balls, due to thepoint or line contact. Therefore, using bevel bolts is characterized bylow wear and greater availability of the entire overload reliefmechanism. Bevel surfaces and complementary V-shaped recesses involverequirements on the manufacturing and assembly accuracy that are lessstringent than with other positive-locking joints, because they are ableto compensate for variations up into the millimeter range.

BRIEF DESCRIPTION OF THE DRAWINGS

The solution to the problem according to the invention will beillustrated hereafter with the aid of the figures, which in detail showthe following:

FIG. 1 illustrates schematically the basic principle of apositive-locking overload relief mechanism against axial overload withthe simultaneous option of transmitting high torques;

FIG. 2 shows schematically another embodiment of an inventionalarrangement for safeguarding against axial force overloads;

FIGS. 3a-3d are side elevational views of various configurations of theinterlocking element wherein each figure shows the element inorientations displaced 90° from each other; and

FIGS. 4a and 4b are sectional views of two different configurations ofthe recesses.

DETAILED DESCRIPTION

FIG. 1 shows a shaft-hub joint 1 for transmission of torques between theequiaxial machine parts--a first machine part 2 and a second machinepart 3--and for realization of axial length equalization. To that end,the shaft-hub joint 1 is fashioned here as a spline joint with slidingfit. The additional arrangement of an overload relief mechanism 4 allowsthe axial movability within the shaft-hub joint 1 only at a specificmagnitude of axial force.

The overload relief mechanism 4 is comprised of at least oneinterlocking unit 5 installed in one of the two machine parts, presentlyin the first machine part 2. The interlocking unit is composed of aninterlocking element 6 and, in the simplest case, a spring 7 and a stop8 that limits the possible prestress force of the spring 7 while forminga structural unit with the interlocking element 6. The spring 7 forcessaid interlocking element 6 into a mating receiving recess or groove 9on the second machine element, thus entering with it into apositive-locking joint. The latter serves to absorb axially directedforces; peripheral forces are not transmitted thereby. Recess 9 can bean annular groove, an elongate or short groove or a recess matching thecontour of element 6. In all cases the recess is bevelled when viewed incross-section.

The number of interlocking elements 6 engaging the machine part 3 on itsperiphery 10 and the adjusted prestress of the springs 7 determine themagnitude of the axial forces that causes the elimination of thepositive locking, that is, the components of the axial forcecounteracting the prestress force of the spring(s) and leading to theelimination of the frictional engagement, always depending on the bevelangle.

Concurring with an axial shift of the second machine part 3, theinterlocking elements 6 shift upon exceeding of the preselected limitvalue of the axial force radially outward, that is, away from the centeraxis I of the two machine parts, thus imparting a further prestress tothe springs 7. The interlocking element 6 shifts according to the shiftof the second machine part 3 against the first machine part 2. Themotion of each individual interlocking element 6 continues in thissimple case until the stop 8 arrives at its limit position, respectivelythe interlocking element has slipped out of its receiving recess 9. Theaxial shift of the machine part 3 toward machine part 2 is made possibleby the axial length equalization by the spline joint 1 with sliding fit.

The explanations to FIG. 1 presuppose that the second machine part 3 islocated on the power output side and thus shifts in axial directionagainst the first machine part 2, which is at least indirectly connectedto the power source. However, also the opposite case is possible--thefirst machine part 2 shifts against the second machine part 3 in axialdirection.

The design of the interlocking unit 4 may vary greatly. As interlockingelements 6, bolts with a head beveled in wedge fashion are givenpreference, since they allow realizing at the points of forcetransmission a large-area contact, which ultimately expresses itself inreduced wear as compared to using balls or cylinder rolls, which allowonly a point contact or line contact at the contact locations in thereceiving recesses. The receiving recesses 9 pertaining to theinterlocking elements 6 are preferably wedge-shaped or coniformdepending on the form of the head of the bolts or pins 6.

The prestress force is preferably applied through spring elements, herea spring 7, the path of the spring element 7 being limited in theillustrated example by the stop 8 in the event of response.

An appropriate design of the interlocking unit 4 contributes topreventing the interlocking elements 6 from sliding back into thereceiving recesses 9. An example of an option for such design ispreviously known from a reprint from "Stahl und Eisen" 108 (1988) No.14/15.

Owing to the low manufacturing expense, spline joints with sliding fitare preferably used to realize a rotationally fixed joint between afirst and second machine part with axial length equalization option.Conceivable as further options, however, are also telescopic designs onantifriction bearings or ball guides.

FIG. 2 shows schematically another embodiment of the inventionalarrangement for torque transmission with axial force limitation. Theoverload relief mechanism in this embodiment is arranged between thefirst, 2, and second machine part, 3, with the first machine part 2supporting at least one interlocking unit 4. The basic structure matchesthat described in FIG. 1, for which reason same references are used foridentical components. The second machine part 3, however, is of atwo-part design. The counterpart required for form-fit is arranged on afirst section 12 of the second machine part 3, which is indirectlyjoined to the second section 11 of the second machine part 3, but has,or allows, a slight axial backlash s relative to it. Called a hollowbody here, this first section 12 features on its outer circumference 13the recesses 9 for receiving the interlocking elements 6. Receivingrecesses 9 are exposed to high stress and thus wear, and therefore anappropriate surface treatment is suitable. For manufacturing and costreasons, the receiving recesses 9 thus are preferably machined intoseparate inserts 14 which are somewhat larger than the receivingrecesses 9 and arranged on the outer circumference of the hollow body.The inserts 14 are then subjected to a separate surface treatment.Normally they are heat-treated, preferably hardened.

The inserts 14 are arranged in corresponding recesses 15 in the outercircumference 13 of the hollow body, and at that, preferably in a waysuch that the outside surface of each insert is flush with the outercircumference 13 of the hollow body 12.

Another option provides only one insert 14 in the form of a two-partring into which the receiving recesses 9 are machined; also conceivableis accommodating the interlocking elements in a preferably V-shaped slotmachined into the two-part ring. The hollow body 12 features then aring-shaped recess 15 extending along the circumference 13 for receivingthe insert.

In this embodiment, spring elements 16, preferably dish springs, arearranged between hollow body 12 and second section 11. This arrangementof the spring elements 16 along with the two-part design of the secondmachine part offers several advantages:

1) Keeping the interlocking elements 6 free of dynamic stresses;

2) Damping in idling and, e.g., during roll change when used in rollingmills;

3) Compensation of small axial strokes.

The hollow body 12 is arranged in such a way that it fits between twocomponents 17 and 18 forming an assembly with the second section 11 ofthe second machine part 3 and an inside surface 19 of the first machinepart 2. A seal is provided at each of the guidance points 20, 21 and 22.

The springs 16 are thus contained in a sealed space 23. Coordinated withthe latter is at least one lubricant feed line, not illustrated here,and one lubricant drain line referenced 24. The arrangement of thelubricant channels is such that the surfaces of the receiving recesses 9will be lubricated whenever an interlocking element 6 disengages therecess. In the embodiment, slight axial forces are absorbed via the dishspring arrangement 16 between the two sections 11 and 12 of the secondmachine part 3, utilizing the axial shift option of the second sectionrelative to the first. In the case of high axial forces, the twosections 11 and 12 shift jointly once the axial shift distance s hasbeen exceeded and the overload relief mechanism responds. Theinterlocking elements 6 slide completely out of the receiving recesses 9and sweep in disengaged state across the outer circumference 13 of thehollow body 12. The lubricant proceeds through the lubricant drainchannel 24 into the interior 25 of the hollow body 12 and from there, bycentrifugal force, through a channel 26 extending through the hollowbody wall and through the insert 14 up into the receiving recess 9, tothe surfaces of the latter.

For the sake of clarity, the embodiment illustrated in FIG. 2 is shownonly schematically without illustrating details and conversion options.Further design details not impairing the function of the embodiment arepossible and may be selected in keeping with known applicationrequirements. Such design of a two-part form of the second machine partis generally possible with any shaft-hub joint featuring apositive-locking overload relief mechanism against axial force. Chosenas interlocking elements, e.g., may be bevel bolts, cylinder rolls,ball-shaped elements etc.

The design of the interlocking unit 4 conforms always to the conditionsof use and the functions to be fulfilled. The embodiment illustrated inFIG. 1 is only an example. Conceivable as well is the use of otherpreviously known interlocking units with the same basic principle.

FIGS. 3a through 3d show examples for the design of interlockingelements 6a-6d in the form of bolts having bevelled head surfaces. Thebevelled surfaces may converge into a wedge (FIGS. 3a through 3d), andthe head may be fashioned, as shown in FIG. 3c, as a truncated wedgesurface. FIG. 3d shows the option of fashioning the bolt 6d with a conichead. The figures illustrating side elevational views of the variousinterlocking elements, i.e., FIGS. 3a-3d, show each interlocking elementin two orientations displaced 90° from each other. The arrows labelledA, B, C and D on the left-hand side of each figure are directed at theside elevation illustrated below the respective letters A, B, C and Dlocated above the interlocking element shown on the right-hand side ofeach figure.

FIGS. 4a and 4b show possible designs of the mount, with the recess incross section. These have cross-sectionally a coniform taper. The mountin FIG. 4a is suited for receiving bolts relative to FIGS. 3a, 3b, 3c;the mount in FIG. 4b for styles according to FIG. 3c. The boltsthemselves, except for the head, may be designed circular ormultipointed in plan view.

The basic principle described here can be employed in any applicationcalling for torque transmission and safeguarding against axial force,for instance in power trains that include jointed shafts or in the caseof jointed or universal shafts. The structural design in detail and theadaptation to particular applications are within the discretion of oneskilled in the art.

What is claimed is:
 1. A shaft-hub joint between two equiaxial machineparts for transmission of high torques in a power train, a first saidmachine part being on a power input end and a second said machine partbeing on a power output end, wherein the two machine parts are joined toeach other in a fashion movable relative to each other but rotationallyfixed relative to each other, said joint comprising:a positive-lockingoverload relief mechanism comprising at least one interlocking oneelement provided between said machine parts locking said machine partsagainst axial thrust up to a given adjustable limit value whereinpositive locking is eliminated when the value is exceeded: saidinterlocking element comprising a head having surfaces beveled in wedgefashion viewed in cross section, said interlocking element supported bysaid first machine part and pressed by a prestress force into areceiving recess in a surface of the second machine part, said receivingrecess machined into a heat treated insert forming an assembly with thesecond machine part.
 2. The shaft-hub joint according to claim 1,wherein said insert is a multi-part ring.
 3. A shaft-hub joint betweentwo equiaxial machine parts for transmission of high torques in a powertrain, a first said machine part being on a power input end and a secondsaid machine part being on a power output end, wherein the two machineparts are joined to each other in a fashion movable relative to eachother but rotationally fixed relative to each other said jointcomprising:a positive-locking overload relief mechanism comprising atleast one interlocking element provided between said machine partslocking said machine parts a against axial thrust up to a givenadjustable limit value, wherein positive locking is eliminated when thevalue is exceeded: said interlocking element comprising a head havingsurfaces beveled in wedge fashion viewed in cross section, saidinterlocking element supported by said first machine part and pressed bya prestress force into a receiving recess in a surface of the secondmachine part; said second machine part having two sections which arejoined to each other indirectly and have an axial backlash relative toeach other; and at least one damping element comprising a dish springarranged between said sections.